Compact X-ray radiograph based on a plasma gun

The results of the experiments on the formation of a plasma emitter with small spatial dimensions for pulsed radiography in the soft X-ray spectral range are presented. Emitting hot plasma was formed as a result of compression of the plasma jet by a current pulse with amplitude I _m = 215 kA and rise time T _fr = 200 ns. For the jet formation, we used a plasma gun based on the arc discharge (I _m = 8.5 kA and T _fr = 6 μs) initiated by breakdown over the surface of a dielectric in vacuum. The experiments were carried out with aluminum, tin, copper, and iron plasma jets. A single emitter, i.e., point Z-pinch (PZ-pinch), was formed when an interelectrode gap of a high current generator of 1.3–1.5 mm was used. The smallest spatial dimensions of the emitting region were obtained with the use of aluminum and tin. For a tin jet, the diameter of the emitting region was 7 ± 2 μm and its height was 17 ± 2 μm. The emission pulse duration at half-height was 2–3 ns. The total emission yield per pulse in the spectral range 1.56–1.90 keV was 30–50 mJ for the aluminum pinch and 10–30 mJ for the tin pinch. The developed method makes it possible to carry out radiographic examination of microobjects (including biological ones) 1–1000 μm in thickness, with spatial (10–20 μm) and time (2–3 ns) resolution.     

Micro- and nanocomposite Ti-Al-N/Ni-Cr-B-Si-Fe-based protective coatings: Structure and properties

A new type of nanocomposite Ti-Al-N/Ni-Cr-B-Si-Fe-based coatings 70–90 μm thick produced by combined magnetron sputtering and a plasma detonation technology is created and studied. Phases Ti₃AlN + Ti₃Al₂N₂ and the phases caused by the interaction of plasma with a thick Al₃Ti + Ni₃Ti coating are detected in the coatings. The TiAlN phase has a grain size of 18–24 nm, and other phases has a grain size of 35–90 nm. The elastic modulus of the Ti-Al-N coating is E = 342 ± 1 GPa and its average hardness is H = 20.8 ± 1.8 GPa. The corrosion rate of this coating is very low, 4.8 μg/year, which is about three orders of magnitude lower than that of stainless steel (substrate). Wear tests performed according to the cylinder-surface scheme demonstrate high wear resistance and high adhesion between the thick and thin coatings.     

Optical and magneto-optical properties of Fe/Cu multilayered films: Influence of the modulation period and the bcc-fcc phase transition in iron

The optical and magneto-optical properties of multilayered film samples of the Fe/Cu system prepared by high-frequency sputtering on an Si(100) substrate are studied by ellipsometry and by measuring the equatorial Kerr effect (the δ _p effect) in the spectral range 0.25–7 μm. The optical characteristics, the plasma frequency ω _p and the relaxation frequency γ ₀ of the conduction electrons, and the δ _p effect are found as functions of the modulation period D=12.5–100 Å. Anomalous behavior of the optical and magneto-optical characteristics is discovered in short-period Fe/Cu structures. The results are discussed within a phenomenological theory of optical and magneto-optical properties for layered structures. Several factors, such as the indirect exchange interaction between the iron layers, the presence of a transition layer on the internal boundaries, the possible “magnetizing” of copper, and the formation of an fcc iron phase in the thin layers, are taken into account in the analysis of the experimental data. Zh. éksp. Teor. Fiz. 112, 1694–1709 (November 1997)     

Investigation of the turbulent mixing of thin layers of materials of different density during the laser acceleration of flat multilayer targets in the Iskra-4 facility

The results of the first experiments devised to investigate the mixing of thin layers of Al and Au during the laser acceleration of flat three-layer targets of Si (5 μm), Al (2 μm), and Au (0.05–0.26 μm) by radiation converted to the second harmonic from the Iskra-4 iodine laser with an intensity of 4×10¹³−7×10¹³ W/cm² (τ _0.5∼1 ns), which acts on the Si side of the target. A method for detecting the occurrence of mixing is developed. It is established that under the experimental conditions the thickness of the mixing region is at least ∼0.15 μm. The results of a theoretical analysis of the evolution of the disturbances leading to mixing are presented. Zh. éksp. Teor. Fiz. 111, 882–888 (March 1997) Deceased.     

Influence of the heater material on the critical heat load at boiling of liquids on surfaces with different sizes

Data on critical heat loads q _cr for the saturated and unsaturated pool boiling of water and ethanol under atmospheric pressure are reported. It is found experimentally that the critical heat load does not necessarily coincide with the heat load causing burnout of the heater, which should be taken into account. The absolute values of q _cr for the boiling of water and ethanol on copper surfaces 65, 80, 100, 120, and 200 μm in diameter; tungsten surface 100 μm in diameter; and nichrome surface 100 μm in diameter are obtained experimentally.     

Pulsed electron-beam melting of a copper — steel 316 system: Evolution of the chemical composition,microstructure, and properties

The surface topography, chemical composition, microstructure, nanohardness, and tribological characteristics of a Cu (film, 512 nm)-stainless steel 316 (substrate) system subjected to pulsed melting by a low-energy (20–30 keV), high-current electron beam (2–3 μs, 2–10 J/cm²) were investigated. The film was deposited by sputtering a Cu target in the plasma of a microwave discharge in argon. To prevent local exfoliation of the film due to cratering, the substrate was multiply pre-irradiated with 8–10 J/cm². On single irradiation, the bulk of the film survived, and a diffusion layer containing the film and substrate components was formed at the interface. The thickness of this layer was 120–170 nm irrespective of the energy density. The diffusion layer consisted of subgrains of γ-Fe solid solution and nanosized particles of copper. In the surface layer of thickness 0.5–1 μm, which included the copper film quenched from melt and the diffusion layer, the nanohardness and the wear resistance nonmonotonicly varied with energy density, reaching, respectively, a maximum and a minimum in the range 4.3–6.3 J/cm². As the number of pulsed melting cycles was increased to five in the same energy density range, there occurred mixing of the film-substrate system and a surface layer of thickness ∼2 μm was formed which contained ∼20 at. % copper. Displacement of the excess copper during crystallization resulted in the formation of two-phase nanocrystal interlayers separating the γ-phase grains. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 6–13, December, 2005.     

Features of materials alloying under exposures to pulsed plasma streams

Surface modifications and features of materials alloying under pulsed plasma exposures are investigated in this paper. The experiments were carried out with a pulsed plasma gun, which generates plasma streams with ion energies of up to 2 keV, a plasma density of (2–, an average specific power of 10 MW/cm² and plasma energy densities in the range of (5–. Nitrogen, helium, hydrogen, oxygen and different mixtures can be used as working gases. Modification of thin (1–2 μm) PVD coatings of molybdenum coating mixed with substrate in liquid phase under the pulsed plasma processing are analyzed. After alloying of ferritic/martensitic steel EP-823 with Mo the concentration of molybdenum in the modified layer of 15–20 μm achieved 20% for single treatment cycle and 30% after two cycles. Decrease of grain sizes (from tens of μm to hundreds of nm), roughness and porosity were obtained by plasma irradiation of thick (~0.1–0.3 mm) plasma sprayed coatings of Co-32Ni-21Cr-8Al-0.5Y and Ti64. A modified layer with homogeneous structure and thickness up to 50 μm is formed as a result of plasma treatment. Mechanisms of surface modification of WC-Co under irradiation with pulsed plasma streams of different ions are discussed.     

Optical properties and electronic structure of YNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

The optical properties of hexagonal intermetallic compounds YNi_{5 − x} Cu _x (x = 0, 1, 2) have been investigated by ellipsometry in the spectral range of 0.22–15 μm. It is shown that the replacement of nickel atoms by copper atoms leads to local changes in the optical-conductivity spectra. A new absorption band is found at 3.5–4.5 eV; its intensity depends on the copper content. The plasma and relaxation frequencies of conduction electrons are determined. The electronic structure and interband optical conductivity of these compounds are calculated within the electron density functional theory using the pseudopotential method. The main parameters of the band structure and the total and partial densities of electronic states are determined. Qualitative agreement is obtained between the experimental and theoretical frequency dependences of the optical conductivity.     

Infrared transmissivity of heavily doped contact layers on extrinsic silicon IR-detectors

The infrared transmissivity of heavily dopedp-type contact layers on silicon was studied in the 3–5 μm and 8–14 μm wavelength range in order to optimise the layer thickness and doping concentration for antireflection coating. The transmissivity of surface layers and buried layers was computed taking into account the free carrier optical dispersion by the Drude theory and corrections due to intervalence band transitions as well as multiple reflections and interferences in the layer. The computations are in quantitative agreement with measurements on contact layers formed by multiple boron implantation. It was found that the free carrier absorption loss completely cancels the gain due to the antireflection effect for a surface layer. Transmissivities of around 73% may be obtained by a buried heavily doped layer.     

A size effect in the optical properties of powdered TiO2

The spectral reflectivity ρ in the region 0.36–2.1 μm and its change Δρ with irradiation by 30 keV electrons versus the average grain sizer _av in a TiO₂ (rutile) powder has been studied in the range 1–7.5 μm. It has been established that the dependence of ρ onr _av differs for different regions of the spectrum, but there is a common increase of ρ in the size range 2.5–4 μm. The value of Δρ after irradiation is also less in powders with this range of sizes. It has been shown that the dependence Δρ=f(r _av) with increasing electron fluence from 2·10¹⁵ to 4·10¹⁶ is strengthened for one band and weakened for another. Tomsk Polytechnic University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 41, No. 12, pp. 52–58, December, 1998.     

Application of Functionalized ZnSe Nanoparticles to Determinate Heavy Metal Ions

In this paper, ZnSe nanoparticles, which were modified with mercaptoacetic acid (MAA), worked as novel fluorescence sensors for the quantitative determination of copper(II) and nickel(II). Under the optimal conditions, the fluorescence intensities of functionalized ZnSe nanoparticles were quenched by the addtion of copper(II) or nickel(II) ions, there were linear relationships between the relative fluorescence intensity (logF₀/F) and the concentration in the range of 140–2,000 μg/L for copper(II) (R = 0.9973) and 30–1,000 μg/L for nickel(II) (R = 0.9992), the limits of detection were 50 μg/L and 5 μg/L, respectively.     

Modeling and analysis of birefringence in magneto-optical thin film made by SiO2/ZrO2 doped with ferrite of cobalt

We report the device characteristics of the metal–dielectric high-reflectivity (HR) coated 1.55 μm laterally coupled distributed feedback (DFB) laser with metal surface gratings by using holographic lithography. The HR coating films are composed of Au/Ti/SiO₂. It provides a variety of advantages compared to the uncoated DFB laser on the same processed wafer while there is no degradation on current–voltage characteristics. For 3 μm wide and 300 μm long HR coated DFB laser, it exhibits a maximum output power of ∼17 mW and a threshold current of 14.2 mA at 20°C under continuous-wave mode. It is clear that the threshold current and slope efficiency are improved by 36% and 96%, respectively, due to the reduction of mirror loss. The metal–dielectric HR coating on one facet of DFB laser is found to have significantly increased characteristic temperature (i.e., T ₀∼88 K). Furthermore, the stable single-mode operation with an increased single-mode suppression ratio was achieved.     

Thermal properties of AlN-based atom chips

We have studied the thermal properties of atom chips consisting of high thermal conductivity aluminum nitride (AlN) substrates on which gold microwires are directly deposited. We have measured the heating of wires of several widths and with different thermal couplings to the copper mount holding the chip. The results are in good agreement with a theoretical model where the copper mount is treated as a heat sink and the thermal interface resistance between the wire and the substrate is vanishing. We give analytical formulas describing the different transient heating regimes and the steady state. We identify criteria to optimize the design of a chip as well as the maximal currents I_c that can be fed in the wires. For a 600 μm thick-chip glued on a copper block with Epotek H77, we find I_c = 16 I_c = 16~A for a 3 μm high, 200 μm wide-wire.     

Femtosecond fiber laser based methane optical clock

An optical clock based on an Er³⁺ fiber femtosecond laser and a two-mode He–Ne/CH₄ optical frequency standard (λ=3.39 μm) is realized. Difference-frequency generation is used to down convert the 1.5-μm frequency comb of the Er³⁺ femtosecond laser to the 3.4-μm range. The generated infrared comb overlaps with the He–Ne/CH₄ laser wavelength and does not depend on the carrier–envelope offset frequency of the 1.5-μm comb. In this way a direct phase-coherent connection between the optical frequency of the He–Ne/CH₄ standard and the radio frequency pulse repetition rate of the fiber laser is established. The stability of the optical clock is measured against a commercial hydrogen maser. The measured relative instability is 1×10⁻¹² at 1 s and for averaging times less than 50 s it is determined by the microwave standard, while for longer times a drift of the He–Ne/CH₄ optical standard is dominant.     

Sensitive detection of temperature behind reflected shock waves using wavelength modulation spectroscopy of CO2 near 2.7?μm

Tunable diode-laser absorption of CO₂ near 2.7 μm incorporating wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) is used to provide a new sensor for sensitive and accurate measurement of the temperature behind reflected shock waves in a shock-tube. The temperature is inferred from the ratio of 2f signals for two selected absorption transitions, at 3633.08 and 3645.56 cm⁻¹, belonging to the ν ₁+ν ₃ combination vibrational band of CO₂ near 2.7 μm. The modulation depths of 0.078 and 0.063 cm⁻¹ are optimized for the target conditions of the shock-heated gases (P∼1–2 atm, T∼800–1600 K). The sensor is designed to achieve a high sensitivity to the temperature and a low sensitivity to cold boundary-layer effects and any changes in gas pressure or composition. The fixed-wavelength WMS-2f sensor is tested for temperature and CO₂ concentration measurements in a heated static cell (600–1200 K) and in non-reactive shock-tube experiments (900–1700 K) using CO₂–Ar mixtures. The relatively large CO₂ absorption strength near 2.7 μm and the use of a WMS-2f strategy minimizes noise and enables measurements with lower concentration, higher accuracy, better sensitivity and improved signal-to-noise ratio (SNR) relative to earlier work, using transitions in the 1.5 and 2.0 μm CO₂ combination bands. The standard deviation of the measured temperature histories behind reflected shock waves is less than 0.5%. The temperature sensor is also demonstrated in reactive shock-tube experiments of n-heptane oxidation. Seeding of relatively inert CO₂ in the initial fuel-oxidizer mixture is utilized to enable measurements of the pre-ignition temperature profiles. To our knowledge, this work represents the first application of wavelength modulation spectroscopy to this new class of diode lasers near 2.7 μm.     

Indentation response of single-crystal copper using rate-independent crystal plasticity

We studied single-crystal copper of three different crystallographic orientations [(100), (011) and (111)] for nanoindentation response via a numerical simulation model using spherical indenters of radius (R) 3.4 μm and 10 μm. The model uses rate-independent crystal plasticity with a finite strain implemented as a user routine in the commercial finite element software ABAQUS. The model takes into account active crystallographic slip, orientation effects during nanoindentation computation, and the effect of friction between the indenter and copper substrate. We compared the load–displacement curve and indentation pile-up patterns obtained from the simulations with experimental measurements available in the literature. The indentation load and mean effective pressure beneath the indenter p _m were found to be highest for (111) orientation and lowest for (100). The simulation and experimental data agree well.     

Carbon nanotubes as nanoparticles collector

This communication reports on a new method for the collection of nanoparticles using carbon nanotubes (CNT) as collecting surfaces, by which the problem of agglomeration of nanoparticles can be circumvented. CNT (10–50 nm in diameter, 1–10 μm in length) were grown by thermal CVD at 923 K in a 7 v/v% C₂H₂ in N₂ mixture on electroless nickel-plated copper transmission electron microscopy (TEM) grids and Monel coupons. These samples were then placed downstream of an arc plasma reactor to collect individual copper nanoparticles (5–30 nm in diameter). It was observed that the Cu nanoparticles preferentially adhere onto CNT and that the macro-particles (diameter >1 μm), a usual co-product obtained with metal nanoparticles in the arc plasma synthesis, are not collected. Cu–Ni nanoparticles, a catalyst for CNT growth, were deposited on CNT to grow multibranched CNT. CNT-embedded thin films were produced by re-melting the deposited nanoparticles.     

Concentration or modulation layering of perfect single crystals Bi2Sr2?xLaxCuO6+δ and Bi2?yPbySr2?xLaxCuO6

Precision structural studies of layering of perfect crystals Bi ₂ Sr _2−x La _x CuO _6+δ (BSLCO) ∼ 10 μm thick, grown by free growth within crystallized melt cavities, detect a macrolayer structure with each layer up to 0.1 μm thick. In the lanthanum concentration range x = 0.6−0.8, only modulation layering is observed. In the concentration range x = 0.3−0.5, either layers with two different lanthanum concentrations, but with the same modulated superlattice type, or layers with the same lanthanum concentration, but with two different modulated superlattice types are observed. At low lanthanum concentrations (0 < x < 0.26), layering into two or even three layer types with different lanthanum concentrations are almost always observed. Modulation suppression when lead is added to a mixture leads to the same layered structure of samples, but with appreciable variations in lattice parameters in the ab plane of individual layers and a and b axis rotation by several degrees with respect to each other in these layers. Thus, the superlattice in BSLCO single crystals stabilizes their composition in the ab plane, and inevitable variations in growth conditions lead to the layered structure of such crystals. Original Russian Text ? V.P. Martovitsky, A. Krapf, 2008, published in Kratkie Soobshcheniya po Fizike, 2008, Vol. 35, No. 3, pp. 29–38.     

The Muonic Hydrogen Lamb Shift Experiment at PSI

A measurement of the 2S Lamb shift in muonic hydrogen (μ⁻p) is being prepared at the Paul Scherrer Institute (PSI). The goal of the experiment is to measure the energy difference ΔE(2⁵ P _3/2−2³ S _1/2) by laser spectroscopy (λ≈6μm) to a precision of 30 ppm and to deduce the root mean square (rms) proton charge radius with 10⁻³ relative accuracy, 20 times more precise than presently known. An important prerequisite to this experiment is the availability of long-lived μp_2S -atoms. A 2S-lifetime of ∼1 μs – sufficiently long to perform the laser experiment – at H₂ gas pressures of 1–2 hPa was deduced from recent measurements of the collisional 2S-quenching rate. A new low-energy negative muon beam yields an order of magnitude more muon stops in a small low-density gas volume than a conventional cloud muon beam. A stack of ultra-thin carbon foils is the key element of a fast detector for keV-muons. The development of a 2 keV X-ray detector and a 3-stage laser system providing 0.5 mJ laser pulses at 6 μm is on the way. This revised version was published online in August 2006 with corrections to the Cover Date.